The present invention relates to a timing system for regulating, via respective camshaft-controlled valves, fluid input and output from one or more cylinders of an engine and/or machine. In particular, the present invention relates to a timing system for varying as required, with the engine or machine running, the lift/rotation strategy whereby the valves are controlled by the cams.
An appropriate way of improving efficiency of internal combustion engines, particularly high-performance engines of sports cars or so-called touring cars, is to vary, according to engine speed/power output/torque, the lift/rotation strategy whereby the cams control the opening/closing cycle of the supply/exhaust valves on the engine. Said lift/rotation strategy is normally imposed by the shape of the lateral cam profile which, when the cam is rotated, gradually cooperates directly or indirectly (via the interposition of rocker arms) with a respective valve stem for determining valve opening/closing speed and acceleration. Variable timing systems have therefore been devised: in the most common type, the cam controlling one or a series of valves is defined by a complex lateral surface, the profile of which varies not only angularly but also axially, so that axial displacement of the cam in relation to the valve provides for varying, in controlled manner, the lift/rotation strategy governing the valve itself. Such a system involves two drawbacks: firstly, it requires complex design cams which are difficult and expensive to produce; and, secondly, it results in axial thrust on the camshaft, in that the axial profile of the cam is arranged obliquely in relation to the valve stem. French Patent n.2.570.123 relates to a variable timing system whereby a single-profile cam controls the valve via a rocker arm having two differently shaped sections. The rocker arm is supported on a mobile arm whereby the cam cooperates selectively with one or other of the differently shaped sections on the rocker arm. Such a system also involves two drawbacks: firstly, the mobile arm supporting the rocker arm is structurally unsatisfactory; and, secondly, the lift/rotation strategy controlling the valve no longer depends solely on the shape of the cam, but also on that of the rocker arm, thus resulting in serious complications both at design and manufacturing level.